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1. Field of the Invention
The present invention relates generally to an electrical device. More particularly the present invention relates to a device for detecting an electrostatic charge on an object and alarming on the potential for electrostatic discharge. An additional action taken on sensing high potential for electrostatic discharge is the use of a positive or negative ion generator to remove the built-up charge.
2. Background Art
Electrostatic discharge between a body or object and an electronic device, such as a circuit board, can damage or destroy the electronic device. Electrostatic discharge can be very dangerous when it occurs during the process of filling a motor vehicle with gasoline, in the vicinity of the gasoline vapors. At other times, electrostatic discharge may cause discomfort. Various devices are used to dissipate an electrostatic electric charge from a body, such as a wrist strap connected to a wire going to ground. Some devices initiate an alarm in the event of an electrostatic discharge. Other devices measure and alarm on static electric charge accumulation. Wilson, in U.S. Pat. No. 6,150,945 reveals a capacitance device for measuring a charge on a body. The device is not grounded and uses a capacitor with a fixed capacitance. A charge accumulates on the fixed capacitance capacitor due to triboelectric processes. The signal, proportional to the charge on the device of U.S. Pat. No. 6,150,945, will tend to decay in magnitude over time due to the use of a high-impedance differential amplifier. This differential amplifier has a finite input resistance, and consequently, discharges the voltage on the very small capacitance produced by a triboelectric charge event.
There is, therefore, a need for a method and device for measuring the electrostatic charge accumulation on a body or object and its potential for electrostatic discharge, all without the inconvenience of a connection to ground. There is a further need for a device for measuring static charge accumulation without causing the signal representing the electrostatic charge to artificially dissipate. A further need is for a method and device for removing an accumulated electrostatic charge from a body or object.
A purpose of this invention is to provide a method and apparatus for accurately measuring an electrostatic charge accumulated on a body or object; and, therefore, the potential for an electrostatic discharge between that body or object and another body or object having a different electrostatic charge and the capacity to change its electrostatic charge. Another purpose of the present invention is to provide a device for measuring electrostatic charge without dissipating the measured charge during the measurement. A further objective of the invention is to provide a method and apparatus for removing an electrostatic charge based on the electrostatic charge measurement results.
To measure a magnitude of electric potential with respect to ground, a capacitance of a conductor having a capacitance to ground is modulated in a periodic fashion. When the capacitance is modulated, the magnitude of the charges on this conductor also changes periodically. The amplitude of this periodic charge is proportional to the electric potential compared to ground.
To effect the above, a rotor is used, having a shape like two identical segments of a circular disk, symmetrical about a pivot point. The rotor oscillates at a fixed frequency about the pivot point with the aid of a torsion spring. One section of this rotor is one plate, or electrode, in the capacitor and oscillates behind a faraday shield in which a hole, or xe2x80x9cwindow,xe2x80x9d is provided. During its travel, this rotor section will pass the window, at one point exposing the greatest surface area of the rotor to the window. It will also pass out of the window such that no part of this rotor section is exposed by the window. Any portion of this rotor section exposed by the window is exposed to the ambient. The electric charge detector experiences its lowest capacitance when this rotor section is completely hidden behind the faraday shield. When the maximum area of this rotor section is exposed to the window, the electric charge detector realizes its greatest capacitance. A second rotor section is an electrically separate conductor used as the movable part, or armature, of an electrostatic motor.
The result of the oscillation and variable capacitance is an Alternating Current (AC) signal, the magnitude of which is proportional to the electric potential applied to the electric charge detector. This signal can also be shown to be proportional to the magnitude of the electrostatic charge potential between the body or object of interest and ground. The polarity of the charge may also be determined by this invention.
When a body or object reaches a threshold charge magnitude, the electric charge detector may be configured to provide an alarm. Such an alarm would be perceptible by one or more of the senses, thus audible, visible, tactile, etc. Another, optional reaction to the detection of an electrostatic charge greater than a predetermined threshold is the generation of positive or negative ions, depending on the sign of the accumulated electrostatic charge, to neutralize the electrostatic charge on the body or object.
The novel features which are believed to be characteristic of this invention, both as to its organization and method of operation together with further objectives and advantages thereto, will be better understood from the following description considered in connection with the accompanying drawings in which a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood however, that the drawings are for the purpose of illustration and description only and not intended as a definition of the limits of the invention.